This invention relates to a method for producing a superlong conjugated polymer.
A diacetylene derivative forms a single principal chain having a .pi.-electron conjugated bond by a polymerization reaction in a solid phase, and forms a polymer of polydiacetylene. Since this polymer possesses electric conductivity and nonlinear optical effects, it is widely studied as an optical and electronic functional material.
Above all, when a diacetylene derivative possessing both hydrophobic group and hydrophilic groups is used, a monomolecular film can be formed on an surface of water, so that the build-up film may be fabricated by the Langmuir-Blodgett (LB) method. Recently, the method had high expectations as being one of the building-up means to develop molecular devices having the aforesaid desirable functions in the molecule itself. According to the LB method, a monomolecular film in the order of tens of angstroms can be produced, and its build-up film may be obtained easily.
Hence, much is studied about the process of polmerizing an LB film using a diacetylene derivative. More recently, it has been disclosed that the photoreactivity of diacetylene derivatives depends greatly on the arrangement of the diacetylene group. Since the role of the side chain group is important for molecular arrangement, photoreactivity is specifically studied on various diacetylene derivatives by replacing the side chain group.
On the other hand, since on many polydiacetylene derivative LB films, the color is changed dramatically from blue to red due to heat, pressure or ultraviolet rays, research is also intensive in studying the phase changes of such films.
However, much is unknown about the photoreactivity of diacetylene derivative LB films. Besides, nothing has been studied about the relationship between the molecular density or molecular arrangement and the photoreactivity in respect to the state of the monomolecular film. Still more, it has not yet been possible to produce straight-chain polydiacetylene of superhigh molecular weight having excellent electric conductivity, i.e. in the production of superlong carbon chains having continuous conjugated bonds.
Accordingly the present inventors, in examining a monomolecular film on the surface of water, i.e., a Langmuir (L) film, have developed a technique capable of optically measuring ultraviolet spectra and other properties at realtime while the .pi.-A curve is monitored, in using such technique, the inventors examined the relationship between the photoreactivity and ultraviolet irradiation of a diacetylene derivative L film and the molecular density or molecular arrangement. Also, the inventors studied the photoreactivity of a diacetylene L film built-up at a typical molecular concentration, and discovered that photopolymerization of an LB film or that the crystals of a diacetylene derivative could produce a compound of only small molecular weight because the molecular area is significantly contracted at the time of polymerization. In other words, if the diacetylene derivative is photopolymerized in the state of an LB film or in the state of crystals, it is impossible to product a straight-chain diacetylene organic polymer which is continuous in respect to the conjugated bonds, as well as superhigh in molecular weight and excellent in conductivity.
On the basis of the above findings, the present inventors attempted to photopolymerize a diacetylene derivative while compressing the derivative at a constant surface pressure always in the state of a monomolecular film on the water surface that is, a Langmuir film (L film). As a result, the inventors finally succeeded in the production of polydiacetylene having continuous conjugated bonds, a straight chain, and which is superhigh in molecular weight (i.e., a superlong conjugated polymer). It has been furthermore discovered that a polydiacetylene of much longer conjugated bonds was obtained when a direct-current bias is applied in the direction of the water surface at the time of said photopolymerization.